The invention relates to improvements in centrifugal worm centrifuges separating liquid/solids mixtures, such as for thickening a thin slurry.
More particularly, the invention relates to an improvement wherein a gaseous pressure medium is introduced into the concentrated sludge in a location preceding the solids discharge opening in the centrifuge bowl. The invention involves operation with a bowl centrifuge wherein the bowl is driven in rotation with a worm therein driven at a speed of rotation different than the bowl. Generally, the bowl will be provided with an axial slurry admission inlet at one end, and the bowl will have an outlet for the liquids fraction at one end and a discharge for the concentrated sludge fraction at the other end. In addition, means will be provided for the introduction at one or more locations of a gaseous pressure medium into the concentrated sludge at a region preceding the solids discharge opening of the basket shell.
Such a worm centrifuge is disclosed in German Published Application 39 21 328 , U.S. Ser. No. 546,237, Filed Jun. 29, 1990, now abandoned. In the foregoing application, the disclosure shows that the discharge of the concentrated sludge from worm centrifuges can present considerable difficulties particularly when the solids to be discharged are soft and have a relatively low viscosity because the soft concentrated sludge can flow back into the treatment part of the worm centrifuge between the helix of the conveyor worm and the inside wall of the conical basket shell part. Proposals have been made to facilitate the discharge of the thick slurry such as by introducing a compressed air into the thick matter in the discharge region of the centrifuge to effectively loosen the thick matter. The quantity of solids discharged as well as the degree of concentration are set during centrifuge operation by varying the differential speed between the basket shell or bowl and conveyor worm of the centrifuge.
In the type of worm centrifuge referred to, an object of the invention is to provide an improved method and apparatus for guaranteeing a reliable independent setting parameter for regulating the desired degree of concentration of the solids discharged from the centrifuge without having to modify the differential speed between the basket shell and conveyor worm that has been optimally set for the best purification of the slurry.
A further object of the invention is to provide an improved method and apparatus for the more effective efficient and reliable operation of a worm centrifuge and thereby obtaining a better capability for a variety of slurries.